This invention relates generally to RF power transistors, and more particularly the invention relates to a laterally diffused MOS transistor (LDMOS) and the method of manufacturing same.
The LDMOS transistor is used in RF applications as a power amplifier. The high frequencies require small dimensions such as gate lengths of less than a micron, thin gate oxide of less than 500 xc3x85, a short channel for cut off frequency (Ft) greater than 10 GH3, reduced source-drain resistance (Rdson), and a high reverse breakdown voltage through use of a lightly doped drain extension.
Conventional manufacturing has limits in realizing these features. Further, the use of sputtered tungsten silicide for a gate contact results in severe shrinkage, causing lifting and reduced gate oxide integrity, and limits gate-drain hot carrier injection improvement. Further, a tungsten silicide and polysilicon gate structure is difficult to etch. Non-planarized field oxide and thick interconnect lines often result.
The present invention is directed to improving the manufacturing process for a LDMOS transistor and providing an improved LDMOS transistor.
In accordance with the invention, a process flow includes the use of nitride masking of the gate structure for a sidewall spacer formation, and the double use of a source and drain mask for dopant implant and for silicide contact formation.
In accordance with a feature of the invention, either titanium or cobalt can be used for the silicide contacts, thereby eliminating the shrinkage associated with tungsten silicide gate.
The invention and objects and features thereof will be more readily apparent from the following detailed description and appended claims when taken with the drawings.